Mineral fibers are used in a variety of products. The fibers can be used as reinforcements in products such as plastic matrices, reinforced paper and tape, and woven products. During the fiber forming and collecting process numerous fibers are bundled together as a strand. Several strands can be gathered together to form a roving used to reinforce a plastic matrix to provide structural support to products such as molded plastic products. The strands can also be woven to form a fabric, or can be collected in a random pattern as a fabric. The individual strands are formed from a collection of glass fibers, or can be comprised of fibers of other materials such as other mineral materials or organic polymer materials. A protective coating, or size, is applied to the fibers which allows them to move past each other without breaking when the fibers are collected to form a single strand. The protection of the size allows the strand to be manipulated in various fabrication processes, such as weaving. Where the fibers are to be used in an industrial application, the size improves the bond between the strands and the plastic matrix. The size may also include bonding agents which allow the fibers to stick together forming an integral strand.
Typically, continuous fibers, such as glass fibers, are mechanically pulled from a feeder of molten glass. The feeder has a bottom plate, or bushing, which has anywhere from 200 to 10,000 orifices. In the forming process, the strand is wound around a rotating drum, or collet, to form, or build, a package. The completed package consists of a single long strand. It is preferable that the package be wound in a manner which enables the strand to be easily unwound, or paid out. It has been found that a winding pattern consisting of a series of helical courses laid on the collet builds a package which can easily be paid out. Such a helical pattern prevents adjacent loops or wraps of strand from binding together should the strand be still wet from the application of the size material. The helical courses are wound around the collet as the package begins to build. Successive courses are laid on the outer surface of the package, continually increasing the package diameter, until the winding is completed and the package is removed from the collet.
A strand reciprocator guides the strand longitudinally back and forth across the outer surface of the package to lay each successive course. A known strand reciprocator is the spiral wire type strand oscillator. It consists of a rotating shaft containing two outboard wires approximating a spiral configuration. The spiral wires strike the advancing strand and direct it back and forth along the outer surface of the package. The shaft is also moved longitudinally so that the rotating spiral wires are traversed across the package surface to lay the strand on the package surface. While building the package, the spiral wire strand oscillator does not contact the package surface. Although the spiral wire strand oscillator produces a package that can be easily paid out, the package does not have square edges. A package having square edges can have a larger diameter than packages with rounded edges. Also, a square edged package can be stacked during shipping. It is desirable to build cylindrical packages having square edges and larger diameters.
A known strand reciprocator which produces square edged, cylindrical packages includes a cam having a helical groove, a cam follower which is disposed within the groove and a strand guide attached to the cam follower. As the cam is rotated, the cam follower and strand guide move the strand longitudinally back and forth across the outer surface of the rotating package to lay each successive course. A rotatable cylindrical member, or roller bail, contacts the outer surface of the package as it is being built to hold the strand laid in the latest course in place at the package edges as the strand guide changes direction. The contact between the roller bail and the rotating package surface causes the roller bail to rotate, and the speed of the roller bail surface is generally equal to the speed of the package surface. An alternative version uses the strand guide itself to contact the package and hold down the strand momentarily at the edge of the package.
To increase productivity, several packages are built simultaneously on a single collet. A separate strand is formed for each package, and a separate strand reciprocator oscillates each strand to build the packages simultaneously. The strand reciprocators are mounted on an arm which moves the strand reciprocators away from the collet as the package radius increases while keeping the roller bails in contact with the package surfaces. The fiber forming process, including the bushing temperature, is controlled to keep the fiber diameters constant throughout the collection process, and to keep the package radii of each of the packages increasing at a similar rate.
Process variations do occur, however, resulting in slight variations in package size along the collet during the collection process. These differences in the relative radii of the packages on the collet cause roller bails to occasionally leave the surface of a package. When a roller bail loses contact with the package surface, the rotational speed of the roller bail begins to decrease. As the surface of the roller bail comes back into contact with the package surface the rotational speed of the roller bail increases until the surface of the roller bail is traveling at the same speed as the surface of the package. Due to bearing friction and the inertia of the roller bail, the roller bail takes time to spin back up to speed. While the roller bail is spinning back up to speed, the difference in speed between the package surface and the roller bail surface causes the roller bail to skid against the package surface. The skidding roller bail produces abrasive forces which can break fibers in the strand if the inertia is too high. In addition, skidding can occur during startup as the rotational speed of the collet is increased. Strand fibers that break tend to separate from the strand as it is wound on the package and wrap around the rotating roller bail, creating a snarl which can ruin the package.
It would be desirable to produce a strand having improved properties for packaging, dispensing and weaving.